In the description of the related art and the description of the invention below, the correlation between the components denoted by the same reference numerals does not indicate that the configurations and the functions thereof are the same as each other, but merely indicates, for example, a partial correlation in function or general designation. Even when the specific configurations or functions are different from each other, the same reference numerals may be given thereto.
In dust produced with various production actions and consumption actions, large dust which may freely fall in the atmosphere and has a diameter of about more than or equal to 10 μm is called dustfall. Dustfall is regarded as a significant form of environmental pollution, and there is a strong demand from society for understanding the actual conditions of the environment and preparing countermeasures. In order to understand the actual conditions of the dustfall, it is important to develop and manufacture an accurate dustfall measurement device. In particular, in the case of setting specific environmental countermeasures, it is effective to adopt a technique of searching for a place causing a problem by the combination of a specific weather condition and a dustfall amount measurement value for a short time corresponding thereto. To perform this method, there is a need to continuously measure the dustfall for a short period of one to ten minutes or less.
Among dust in an atmosphere, minute dust having a diameter of 10 μm or less and floating in the atmosphere substantially without falling freely is called a suspended particulate matter (SPM). Since the SPM substantially moves in accordance with the ambient atmospheric flow, only the concentration of the SPM in the atmosphere may be considered as a problem in the environmental influence evaluation of dust. For this reason, in the case of measuring the actual state of the SPM in the atmosphere, for example, a constant amount of atmosphere is suctioned and filtered, whereby the concentration of the dust in the atmosphere is calculated. On the other hand, the larger dustfall does not move completely in accordance with the ambient atmospheric flow. The dustfall falls in the atmosphere at a different speed in accordance with the density or the size of the particle so as to be deposited on the ground. When there is a barrier in the atmosphere, the dustfall collides with the barrier and adheres thereto. For this reason, the environmental influence of the dustfall mainly occurs due to contamination caused by the deposition or the adherence of the dustfall to a specific material. Therefore, in order to evaluate the environmental influence of the dustfall, it is not sufficient to only measure the concentration of the dustfall in the atmosphere, and there is a need to measure the amount of the dustfall passing through a unit area of an inspection plane fixed to a space per unit time, that is, the flux of the dustfall.
The flux of the dustfall, which is a subject of the environmental problem, may be divided into a vertical flux and a horizontal flux. In the vertical flux, the inspection plane is horizontal, and is mainly concerned with the evaluation of the deposition of the dustfall on the ground. In the horizontal flux, the inspection plane is vertical, and is mainly concerned with the evaluation of the adherence of the dustfall to a vertical surface such as a wall of a building. The atmospheric flow outside a building, that is, wind may be regarded as having a vector in the horizontal plane according to an average for a long period of time. For this reason, the vertical flux is not influenced by the wind speed. On the contrary, the horizontal flux is a function of the wind speed. More specifically, the flux of the dustfall may be defined by the following equation.[vertical flux of dustfall]=[concentration of dustfall]×[falling speed of dustfall][horizontal flux of dustfall]=[concentration of dustfall]×[wind speed of component perpendicular to inspection plane]
Likewise, in order to measure the horizontal dustfall flux, there is a need to understand the wind direction or the wind speed during measurement at all times. Furthermore, the measurement device needs to have a function of collecting the flow of the dustfall in the wind direction at all times. On the other hand, in the measurement of the vertical flux of the dustfall, such consideration is not needed, and the horizontal dustfall flux may be measured in a simpler manner. For this reason, in the public management of dustfall, a device solely measuring the vertical flux, for example, a deposit gauge shown in FIG. 1 has been used. In the deposit gauge, a dust sampling port 1 is formed in a trumpet shape which is opened upward. The dustfall is collected in a manner such that the dustfall falling and deposited on the inner surface of the dust sampling port 1 is made to flow into a collection container 25 present below the dustfall sampling port 1 by rainwater or water used for collecting the collected dustfall.
Further, the horizontal dustfall flux may be formally transformed from the vertical flux in the following equation.[horizontal flux of dustfall]=[vertical flux of dustfall]×[wind speed of component perpendicular to inspection plane]/[vertical falling speed of dustfall]
Here, the wind speed of the component perpendicular to the inspection plane is defined as below. First, a virtual inspection plane is perpendicularly installed at a point which causes a problem. At this time, the wind speed of the component perpendicular to the inspection plane is a component in accordance with the direction perpendicular to the inspection plane in the wind speed at the point.
For this reason, even when the horizontal dustfall flux is regarded as a problem, a simple evaluation using the measurement result of the vertical flux and the equation has been conducted. However, in fact, it is difficult to quantitatively measure the falling speed of the dustfall variously changing with time. For this reason, a large error occurs when calculating the horizontal flux of the dustfall on the basis of the equation. Therefore, when the horizontal flux is a problem, it is desirable to directly measure the horizontal flux from the viewpoint of measurement precision.
As a dustfall trapping device that directly measures a horizontal flux of dustfall, a device is disclosed which naturally circulates wind inside a dust sampling port 1, traps dustfall by collecting a portion of the dustfall introduced with the wind through inertial dust collection or gravitational dust collection, and measures the horizontal flux of the dustfall according to the result. Non-patent Document 1 discloses a plurality of particle trapping devices of this type.
As the representative type, a big spring number eight (BSNE) is shown in FIGS. 2A and 2B. In the BSNE, an atmosphere naturally flowing from an external air inlet 10 into the dust sampling port 1 is decelerated inside the device as the flow passage is widened. Subsequently, as depicted by a flow line of an atmospheric flow 17 passing through the dust sampling port, the atmosphere naturally flows outward from an exhaust port 8, which is a metallic mesh provided on the top surface of the device. The wind decelerates inside the dust sampling port, so that the retention time of the dustfall inside the dust sampling port 1 increases, and the dustfall falls freely by a long distance inside the dust sampling port in the meantime.
Likewise, the portion inside the dust sampling port 1, exhibiting an effect of reducing the wind speed inside the dust sampling port so as to be lower than the wind speed of the flow 15 of the external air so as to increase the retention time of the dustfall inside the dust sampling port 1 and increasing the falling distance of the dustfall, is referred to as a wind reduction area 13 in the specification.
The dustfall in the atmosphere falling in the wind reduction area 13 falls freely or collides with the wall of the downstream end of the device when passing through the inside of the device as depicted by the flow line of trapped dustfall 19. Subsequently, the trapped dustfall 19 passes through a metallic mesh 33 disposed below the flow passage and is trapped by a particle trap 32.
A portion of the dust inside the dust sampling port 1 flows into the external air from the exhaust port 8 as depicted by the flow line of dustfall 20 passing through the dust sampling port. Further, the entire device is rotatable in the horizontal direction, and the external air sampling port 10 is made to be automatically directed toward the upward wind direction at all times due to the action of a blade 23 and a rotary shaft 24 provided in the device. Even though this device really has a simple structure, the trapped dustfall is manually collected at one time. For this reason, in the BSNE, it is difficult to continuously measure the transition of the time-series dustfall trapping amount for a short period.
Further, in the BSNE, the dustfall trapping surface is long and large along the wind direction. For this reason, it is difficult to accumulate the dustfall in a narrow space area to increase the concentration of the dustfall. Further, it is difficult to further provide a device highly precisely measuring the dustfall amount, for example, the dustfall mass in the BSNE. This is because the mass of the trapped dustfall is much smaller than the mass of the BSNE body as the trapping device. For this reason, it is essential to independently measure only the mass of the dustfall after spatially separating and concentrating the dustfall from the BSNE body.
Non-patent Document 1 introduces a suspended sediment trap (SUSTRA) or a Modified Wilson & Cooke sampler (MWAC) as the collector for the horizontal dustfall flux. The collection principle of the SUSTRA is basically the same as that of the BSNE. The MWAC dust sampler shown in FIGS. 7A and 7B includes: a collection bottle with an external air inlet 10 which is an L-shaped pipe having an opening provided in the upward wind direction; and an exhaust port 8 which is an L-shaped pipe having an opening provided in the downward wind direction. The MWAC does not have a special mechanism that makes the external air inlet 10 of the dust sampling port follow the wind direction.
In order to continuously measure the horizontal flux of the dustfall, as described above, the trapped dustfall needs to be concentrated at a narrow space area to increase the density thereof, and the dustfall needs to be introduced into a certain continuous dust amount measurement device 6. In order to exhibit such an effect, the dustfall in the atmosphere needs to be introduced into the dust sampling port 1 together with the atmosphere, and air containing the dustfall inside the dust sampling port 1 is suctioned so as to be introduced into the continuous dust amount measurement device 6. During a time in which the dust is suctioned, the continuous dust amount measurement device 6 continuously measures the dustfall amount per unit time.
As described above, the dustfall does not completely move in accordance with the flow of the wind. For this reason, for example, in the dust sampling port 1 of the dustfall amount measurement device, the suction may be performed in the direction different from the wind direction as shown in FIG. 3 or the suction may be performed at a speed different from the wind speed as shown in FIG. 4. In this case, suctioning of the dustfall in the external air to the dust sampling port 1 together with suctioned atmosphere 16 is not limited thereto. As in the dustfall 18 in the external air of FIGS. 3 and 4, the ratio of the dustfall bypassing the external air inlet 10 is large to a degree which may not be ignored. Furthermore, the ratio of the bypassing dustfall is sensitively influenced by various weather conditions, characteristics of the dustfall, and the shape of the device. For this reason, it is difficult to predict the ratio of the bypassing dustfall.
Therefore, the suction type shown in FIGS. 3 and 4 is not desirable as the dustfall collection method for measuring the horizontal dustfall flux. Specifically, such a dustfall sampling method is shown in Patent Documents 1, 2, and the like. In these devices, since the external air suction speed is constant in the external air inlet 10 at all times, the wind speed of the external air is generally not equal to the external air introduction speed.
Further, the direction of disposing the external air inlet 10 is generally fixed in many cases. Therefore, the normally changing wind direction of the external air is not generally equal to the direction of the external air inlet 10. For this reason, as disclosed in Non-patent Document 4, the dust trapping efficiency of the particle having a diameter more than 10 μm in this type of dust sampling port 1 is extremely small such as to be a several % or less.
Further, since the dust trapping efficiency is strongly influenced by the ambient measurement conditions such as a wind speed, it is difficult to highly precisely understand the outdoor dust trapping efficiency. For this reason, in the dust sampling port 1 collecting the atmospheric dustfall in order to measure the horizontal dustfall flux, there is a need to introduce an atmosphere at substantially the same speed as the wind speed and the wind direction of the external air.
In a dust trapping method of introducing an atmosphere into the dust sampling port 1 at the same speed as the wind speed and the wind direction of the external air, there is a method called uniform suction. In the uniform suction, the wind speed of the external air is measured, and a suction flow rate of a separate blower is controlled so that the atmosphere introduction speed at the inlet of the dust sampling port 1 matches the wind speed. This method is mainly applied to the case of measuring the flux of the dust inside a wind tunnel of which the wind direction is fixed as shown in the example of Non-patent Document 2. Patent Documents 4 and 5 disclose a method of controlling the direction of the dust sampling port 1 so that the direction matches the wind direction at all times in accordance with the control of the wind speed at the time of applying the uniform suction to trap the dustfall outdoors for the purpose of obtaining the horizontal flux of the dustfall. Such a method is the most reliable method of trapping the dustfall concerned with the horizontal flux measurement. However, in this case, a complex configuration and a complex control are needed due to a flow rate control device or a rotation mechanism of the dust sampling port, and the device may easily become expensive and increase in size. For this reason, this can not be considered a simple measurement method.
Further, weather resistance is an important function for continuously measuring the horizontal flux of the dustfall for a long period at an outdoor place. In particular, a problem such as a failure occurs in many continuous dust amount measurement devices when raindrops intrude into a measurement unit in the case of rainfall. Therefore, there is a need to provide a structure capable of preventing raindrops from intruding into the dust sampling port 1 or removing raindrops intruding into the dust sampling port 1. In general, a manual simple dust trap such as the BSNE does not include a mechanism of preventing raindrops from intruding into the external air inlet 10 or a mechanism of removing raindrops inside the device.
As a method of preventing raindrops from intruding into the dust sampling port 1, there is known a method of providing a louver in the dust sampling port 1 or a method of Patent Document 1. In the device of Patent Document 1, the dust sampling port 1 has a structure shown in FIG. 4. In addition, an impactor is provided so as to remove dustfall or raindrop with a diameter more than 10 μm. However, as for the principle of preventing raindrops from intruding into the dust sampling port 1 of this method, the flow passage of the atmosphere flowing into the dust sampling port 1 is abruptly changed to remove raindrops which may not follow the atmospheric flow. For this reason, in this method, large dust such as dustfall is removed together with the raindrops inside the dust sampling port 1. Therefore, this method is not suitable as a method of trapping dustfall according to the object of the invention.
Next, the continuous dust amount measurement device of the related art will be described. As the continuous dust amount measurement device, various types are proposed. The simplest method is a low volume sampler shown in Non-patent Document 3. In this device, the dustfall in the suctioned atmosphere is filtered by a filter, and a variation in weight of the filter is measured off-line so as to calculate the mass of the trapped dust. In the case of this device, the filter needs to be replaced after a short period in order to perform the continuous measurement. For this reason, this method is not practical from the viewpoint of burden of work. Furthermore, a device increasing the suctioned flow rate of the low volume sampler for the measurement at a short time is called a high volume sampler. Therefore, the principle, the structure, and the reliability of the high volume sampler are substantially the same as those of the low volume sampler.
Further, Patent Document 6 discloses a continuous dust amount measurement device shown in FIG. 5. In this device, a trumpet-shaped dust sampling port 1 with an upward opening is provided, so that the dustfall may be trapped and the mass of the dust may be continuously and precisely measured using a β-line absorption type mass measurement device.
In this device, the atmosphere flowing into the dust sampling port largely and rapidly turns inside the dust sampling port, and most of the atmosphere advances along the flow passage 17 so as to flow to the outside of the system. When the wind speed of the external air increases, the amount of the dustfall flowing into the dust sampling port 1 also increases, but the turning flow speed inside the dust sampling port 1 also increases in proportion to the wind speed. As a result, the amount of the dustfall flowing to the outside of the system from the inside of the dust sampling port increases. For this reason, the dustfall trapping efficiency is hardly influenced by the wind speed of the external air, and the vertical flux of the dustfall may be suitably measured. However, this device is not suitable for the measurement of the horizontal flux of the dustfall. In the device, a failure may occur in the device when suctioning raindrops in many cases. For this reason, generally, this device includes a mechanism automatically covering the opening of the dust sampling port 1 in the case of rain, and does not perform the measurement in the case of rain.
Further, Patent Document 7 discloses a particle counter 11 which is a light scattering type particle counter. This device is operated in accordance with the principle in which each dust particle passing through a measurement unit is irradiated with a laser beam and the reflection and the intensity of the scattered light are detected so as to determine the presence of dust particles with a predetermined diameter or more. This device may measure the number of dust particles in the suctioned atmosphere. However, when a standard sample of dust is separately provided and a relationship between the number of dust particles and the mass of dust is determined in advance, the number of dust particles detected at the particle counter 11 may be converted into the mass of dust.
Further, since there is no need to trap the dust in this device, a filter need not be essentially provided. Furthermore, a device is also available which sprays sheath air corresponding to clean air to the periphery of the suctioned external air in the same axis as that of the flow of the external air. Accordingly, dust or fog dip contained in the suctioned external air may be collected inside a measurement flow passage. However, there is a problem in that a failure occurs in the device when suctioning a large amount of raindrops as in the above-described other devices.
Further, Patent Document 8 discloses a light transmission type particle concentration meter. In this device, dust suctioned together with atmosphere inside the device is irradiated with light. At this time, the light transmission amount of the light attenuated due to the effect of the reflection or absorption of the dust is measured and converted into the concentration of the dust. The weather resistance is the same as that of the particle counter 11.